Upgrade as many internal pieces as possible. 16gb ram and as large of an SSD as she needs (assuming both of these can be upgraded). I would try and leave about 50gb of free space in it. I dont know off hand what type of ram you will need but im sure someone does. Cleaning out the inside (use a air compressor or air spay canister, and try not to let the fan(s) spin. If you are feeling really technical you can pull the cooler off and get some new thermal paste.
A fresh install of MacOS would be good too. Dont let it keep files and manually reinstall everything she needs (of course, back all the data up first).